Plastic containers are used for the packaging of items, such as food or other products. A plastic film or a lid may be bonded to the plastic container thereby obtaining a closed package containing the product.
In accordance with a first technique a lid may be applied to a container by heat bonding of the lid to the top rim of the container. For example, EP0469296 discloses an induction sealing apparatus configured for sealing a plastic lid to a plastic container. The apparatus includes a nest having a recess for holding a container to be sealed, and a movable sealing head configured for holding a precut and flat lid and for positioning the lid relative to an opening in the container. An induction coil mounted in the sealing head induces a heating electrical current in the lid to seal the lid to the container. This solution is not adequate to packaging of products protruding above the top rim of the container because the lid is flat and the apparatus is configured to handle flat lids only.
A second technique, known as vacuum skin packaging is employed for packaging food products. Vacuum skin packaging is described for instance in FR 1 258 357, FR 1 286 018, AU 3 491 504, U.S. Pat. No. RE 30 009, U.S. Pat. No. 3,574,642, U.S. Pat. No. 3,681,092, U.S. Pat. No. 3,713,849, U.S. Pat. No. 4,055,672, U.S. Pat. No. 5,346,735 and WO2011/012652.
Vacuum skin packaging is basically a thermoforming process. In particular, the product is placed on a support (such as a tray, a bowl or a cup) and then the support with the product placed thereon is put in a vacuum chamber, where a film of thermoplastic material, held by vacuum in a position above the product placed on the support, is heated to soften it. The space between the support and the film is then evacuated and finally vacuum above the film is released to cause the film to drape down all around the product and seal to the surface of the support not covered by the product, thus forming a tight skin around the product and on the support.
In the case of a product protruding above the edge of the tray, the film holder may be concave and e.g. shaped as a dome in order to host the protruding portion of the product during application of the plastic skin.
For instance, in order to package a bulky product having a portion protruding from the tray top rim, US 2005/0257501 shows a device consisting of an upper tool and a lower tool. The upper tool comprises an internal space in which a forming device with a concave opening facing the lower tool is fixedly mounted. A sealing tool is provided which is movable from the retracted position into the sealing position and a cutting blade which is surrounding the sealing device and which is also pneumatically movable from the retracted position to the cutting position as shown in and back is provided. After film and tray positioning, an evacuating is performed above the upper film having the consequence of the upper film being sucked to the inner wall of the forming device and thus being stretched. After the upper film is sucked to the internal surface of the forming device, the sealing tool is moved into the sealing position and thereby the edge of the tray and the upper film are sealed hermetically. Subsequently, the cutting blade is operated and thereby the completed package is separated from the upper film layer. Although this apparatus may be used for packaging products protruding above the top rim of the tray, it should be noted that the described apparatus is suitable for products of a same standardized size.
In US3694991 a vacuum skin packaging apparatus capable of packaging products above a flat board is described; according to this document the product on the flat board is placed in a vacuum chamber and a sheet of thermoplastic film is placed above the product. A portion of the film is drawn against the concave interior surface of the upper portion of a vacuum chamber; the film is then heated by surface contact; and then, after evacuation of the chamber, air pressure is used to blow the film down over the product and against the flat board. The height of the chamber may be adjusted before execution of the above cycle by locating an adapter between the upper and the lower portions of the vacuum chamber. Although the described apparatus allows packaging of different products, adjusting the height of the vacuum chamber is not practical and, additionally, the specific design of this apparatus is not adapted to packaging of products in trays, let alone of bulky products.
Thus it is an object of the invention conceiving a packaging process and a packaging apparatus which can overcome the limitations of the known solutions described above.
In particular, it is a main object of the invention, to offer a packaging process and a packaging apparatus which may effectively adapt to packaging of products protruding above the support or tray and still be able to effectively package products not emerging above the respective support or tray.
A further object of the invention is a packaging process and a packaging apparatus configured to packaging products of different sizes and degrees of protrusion above the respective support or tray.
In particular, it is an object of the invention to provide a packaging process and a packaging apparatus adapted to packaging of products having a high degree of protrusion above the support or tray.
An ancillary object of the invention is a packaging process and a packaging apparatus capable of adapting to product protrusions of various geometries and in particular to products having protrusions located in the vicinity of tray or support top rim.
Another auxiliary object of the invention is to offer a packaging process and a packaging apparatus having the ability to reduce imperfections, such are plies or wrinkles, on the film applied to the product and thus improve the appearance of the final packaged product.
Moreover, it is another object of the invention to offer a packaging process and a packaging apparatus adapted for skin packaging of products.
Another object is that of offering a process and an apparatus capable of increasing productivity, without negatively impacting on the quality and reliability of the packaging.